Recepteur d'Origine Nantais Tyrosine Kinase Is a Direct Target of Hypoxia-inducible Factor-1α-mediated Invasion of Breast Carcinoma Cells

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) overexpression was shown to be associated with invasion and metastasis of tumors and tumor cell lines. The identification of molecular targets that contribute to HIF-1 alpha-mediated invasion is under intensive investigation. We have analyzed the role of recepteur d'origine nantais (RON), a tyrosine kinase receptor for macrophage-stimulating protein (MSP) that plays a role in breast cancer cell invasion as one of the molecular targets of HIF-1 alpha. Analysis of a panel of breast cancer cell lines indicated a correlation between HIF-1 alpha and RON expression. Treatment of HIF-1 alpha-and RON-positive breast cancer cells with HIF-1 alpha inhibitor, echinomycin, led to the inhibition of HIF-1 alpha activity and RON expression. We have identified HIF-1 alpha binding site on the RON promoter. Chromatin immunoprecipitation analysis and site-directed mutagenesis of the RON promoter confirmed the binding of HIF-1 alpha to RON promoter. HIF-1 alpha inhibitor-, echinomycin-, or short hairpin RNA-mediated selective knockdown of HIF-1 alpha or HIF-1 alpha target RON tyrosine kinase abrogated RON gene expression, and the RON ligand macrophage-stimulating protein mediated invasion of breast cancer cells. Consequently, the data presented herein demonstrated RON as a novel molecular target of HIF-1 alpha and suggest a potential therapeutic role for HIF-1 alpha or RON tyrosine kinase inhibitors in the blockade of RON tyrosine kinase-mediated invasion of carcinoma cells.